Conventional golf balls can be divided into two general classes: solid and wound. Solid golf balls include one-piece, two-piece (i.e., single layer core and single layer cover), and multi-layer (i.e., solid core of one or more layers and/or a cover of one or more layers) golf balls. Wound golf balls typically include a solid, hollow, or fluid-filled center, surrounded by a tensioned elastomeric material, and a cover.
Examples of golf ball materials range from rubber materials, such as balata, styrene butadiene, polybutadiene, or polyisoprene, to thermoplastic or thermoset resins such as ionomers, polyolefins, polyamides, polyesters, polyurethanes, polyureas and/or polyurethane/polyurea hybrids, and blends thereof. Typically, outer layers are formed about the spherical outer surface of an innermost golf ball layer via compression molding, casting, or injection molding.
From the perspective of a golf ball manufacturer, it is desirable to have materials exhibiting a wide range of properties, such as resilience, durability, spin, and “feel,” because this enables the manufacturer to make and sell golf balls suited to differing levels of ability and/or preferences. In this regard, playing characteristics of golf balls, such as spin, feel, CoR and compression can be tailored by varying the properties of the golf ball materials and/or adding additional golf ball layers such as at least one intermediate layer disposed between the cover and the core. Intermediate layers can be of solid construction, and have also been formed of a tensioned elastomeric winding. The difference in play characteristics resulting from these different types of constructions can be quite significant.
Ionomers produce materials having excellent toughness, crack resistance, resilience, and a wide range of hardness values and moduli, which make them ideally suited for golf ball layers. Unfortunately, many of the most useful properties of ionomers are achieved only at high levels of crosslinking, which can render the composition intractable and difficult if not impossible to process into a working part or layer due at least in part to their very low melt flow properties. In related U.S. application Ser. No. 15/955,770 of Comeau et al., hereby incorporated by reference herein in its entirety, mixtures of ionomer(s) and/or precursor(s) with at least one polyethylene, at least one polymeric epoxy crosslinker and at least one compatibilizing polymer synergistically created a melt processable composition without sacrificing coefficient of restitution, compression, Shore D hardness and Shore C hardness. In these mixtures, a discrete, discontinuous, highly crosslinked ionomer/precursor and polymeric epoxy crosslinker portion was dispersed throughout and contained within an inert, moldable thermoplastic continuous phase containing at least one polyethylene and at least one compatibilizing polymer.
However, there is still a need to develop highly cross-linked ionomers that are moldable yet possess some of the beneficial properties of rubbers, and meanwhile without sacrificing desirable CoR, compression and hardness (both Shore D and Shore C). Golf balls of the invention and methods of making same address and fill this need.